Electron lens system



May 14, 1946. c. H. BACHMAN ELECTRON LENS SYSTEM Filed 0.01;

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Patented May 14, 1946 UNITED jsTATas 0ppm Ej li Charles H. Bachman, Scotia; N. Y., assignor to` Generali Electric Company; a corporation ofi NewYork Application October 2K5, 1943 Serial No. 507,557

(Cl. Z50-162)v 4 Claims.

The present: invention relates to; a cathodev ray tube and: it: has for its' object to: provide ,ann irnprovedv electron lens system for such a tube;

In a cathode ray device, such as an'electron microscope in which a visible image is formed by the action:` of an electron stream, it is customary to use an electrostatic lens system inthe form of a plurality of apertured` metallic disks, axially aligned and spaced, and the center disk operating atv a potential differing from. that off the outer ones. Oneof the problems inthe construction of an electron lens of this type is that' otY maintaining very accurate alignment oftheelements and, at the same time, insulating one'or more elements from the rest. In particular, inlens systems of this type Where the central disk operates at a high voltage with respect to'- the remaining disks and their'enclosing envelope, the problem of suitably insulatingvthe system assumes major proportions. Factors which must be' considered in insulating such a lens are'the surface of the insulator and its volume leakage', the character of the surfacef'rom the standpoint of the charges building up on it, and the gas evolution, the dielectric structure of theinsulator,A and its ease oi assembly in the cathode ray device. It is an object of the present invention toA provide an improved insulating' means for an electrostatic lens system. l

The foregoing object is accomplished in accordance with one embodiment of the inventionjby providing a vitreous insulator which extends around substantially the entire periphery ofthe lens member operating at a high potential' with respect to the enclosing envelope, but which conz tacts said member andthe enclosing envelope at a. minimum number of spaced points to increase the length of the insulating path while reducing the insulator area. It is found that, in the .use of the invention in an electron microscoperthe operating potential of the lens system may be increased substantially, while the task of assembling the lens system in the microscope is reduced.

The features which I desire to protect herein are pointed out with particularity in the appended claims. The invention itself may best be understood by reference to the following description taken in connection with the accompanying drawing, in which Fig. 1 shows schematically a lens n system of the type considered in the present invention; Figs. 2 and 3 are cross-sectional and end views, respectively, of an electron lens system embodying certain features of the invention; and Figs. 4 and 5 illustrate other embodiments of the invention.

InFig. 1, there-is shown an electron flens. sys.- tenr comprising three apertured metallic disks m3, i t, |22, axially aligned and spaced. The disks are provided, respectively, with central apertures lf3, E4i tthrough. which is'projecteda cathode ray beam represented bythe arrow i6 andwhich istebe deflected by the electron lens system'.-

passingithrough the` aperture I3, are made to. converge through the action of the highly repellent electrostatic: eld. createdb-y the lens' member l I.

In-.Figs'. 2.7and;v 3, there isl shownV a portion of an electron microscope employing an electron; lens system: oi the type illustrated in Fig. V1.k The electron microscope includes av cylindrical metallic envelopeV t8! in'which 'the disksv lil--IZ- rare supported.. Thetwo outer disks I0, l2 are machined- 'toitsnuglyl within the envelope i8.. Thel central `rectrode lli isheld between two parts i9', 2B' of a .ring insulator constituted ofany suitable dielectric materiall, such as for example glass or Micalex; The parts I9' and 2%] are machined on then-outer edges te yconform to theY inner diameter oi`r envelope Il!y andare provided on their inner edges with grooves 2l for engaging the outer edge oiv electrode ll`.

I-nvassembly of the electron lens system within the envelope i8', a pair of cylindrical spacers 22 andA 23 are interposed, respectively, between the parts I9 andl 2-0 and: the" disks It and '42. An

additional pair of cylindrical' metallic spacers 24, 25 engage the'opposite faces oi disks I8 and l2 to Vmaintain these disks in spaced relation with other' elements'of the electron microscope. In this composite electron lens structure; the insuflati'n'g parts' 19j 2l) maintain the electrode H centrally aligned Within envelope i8, as well as insulate this electrode from the envelope andthe electrodes i9 and l2 so that electrode Il maybe operated at a high negative potential. At the same time, the spacers 22, 23 maintain the electrodes in a desired axial spacing. As shown in Fig. 3, the electrode I0 is provided with aperture 26 through which extends a tubular conductor 21 connected to the outervedge of disk Il to supply this disk with the high negative potential at which it operates.

Where it is desired to operate the electrode Il at very high potential with respect to the remaining parts of the electron system, the surface tions of the insulator member 3|! adjacent the points 3| are grooved to engage the outer edge of lens member in the same manner as the grooves 2| of the insulators I9 and 2|) in the structure of Fig. 2. The insulator 30 is machined at the points 32 to conform to the inner diameter of envelope |8.

In one method of constructing the insulator 3D, I

an ordinary cane glass rod is used and is bent on a ilat surface or plate around spaced pegs set in the plate to obtain a desired configuration of the insulator. With this construction, the insulator path between the points of Contact 3| and 32 with the electrode l l and the envelope I8 is increased to permit the use of higher voltages between these elements of the lens. Moreover, since the glass insulator 3B possesses a certain amount of resiliency, the open ends 34, 35 may be sprung apart slightly to permit insertion of lens Il into the grooves at points 3| prior to assembly into the envelope I8. This type of insulation may also be molded or machined to the desired shape. Also, any suitable insulating material other than glass may be used, for example, porcelain or steatite.

A still further variation useful in certain cases is shown in Fig. 5, in which a configuration of the insulator 30 differing slightly from that of insulator 3i) is obtained. The insulator 39 is shown as a small surface area in contact with the lens I at the'points 3 while the number of such points has been reduced, thereby permitting' the use of even still higher voltages in connection with the electron lens system. In this embodiment, the insulator 3S' provides a three-point suspension of the disk i I within the lens system.

The invention described herein may be used to advantage in cathode ray devices in permitting the employment of potentials on an electron lens system which have previously been found impossible because of the breakdown of the insulators required in such systems. Numerous additional modications may obviously be made in my invention and I aim in the appended claims to cover all such variations as come within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. A lens system for an electron microscope of the type including a cylindrical metallic envelope, said system comprising three parallel disk-like metallic members having aligned central apertures, the outer of said members being in contact with said envelope throughout substantially their entire circumference, insulating means contacting said envelope and the third of said members at a plurality of points for supporting said third member transversely to the axis of said envelope, and cylindrical spacers interposed between said insulating means and said vouter members, said insulating means contacting said third member solely at the outer edge of said member, whereby the region between said third member and said outer members may be substantially completely evacuated, said insulating means and said third member being substantially coplanar whereby said third member may be operated at a high potential with respect to both said envelope and said outer members. l

2. In a cathode ray tube having a metallic envelope and a centrally apertured metallic disklike lens member maintained at a substantial voltage with respect to said envelope, an insulator for supporting said lens member within said envelope comprising a rod member extending around substantially the entire periphery of said lens member and contacting said envelope and said lens member at a plurality of spaced points, the cross-sectional area of said rod member being substantially smaller than the distance between the outer edge of said lens member and the inner surface of said envelope to reduce the area of the insulator path between said lens member and said envelope.

3. In a cathode ray tube having a metallic envelope and a centrally apertured metallic disklike lens member maintained at a substantial voltage with respect to said envelope, an insulator for supporting said lens member within said envelope comprising a vitreous rod extending around substantially the entire periphery of said lens member and contacting said envelope and said member at a plurality of spaced points, the crosssectional area of said rod being substantially smaller than the distance between the outer edge of said lens member andthe inner surface of said envelope, said rod being adapted at its points of contact with said lens member to engage the outer edge of said member.

4. In a cathode ray tube having a metallic envelope and a centrally apertured metallic disklike lens member maintained at a substantial voltage with respect to said envelope, an insulator for supporting said lens member within said envelope comprising a rod of insulating material extending around substantially the entire periphery of said lens member and contacting said envelope and said member at a plurality of spaced points, said rod being adapted at its points of contact with said lens member to engage the Outer edge of said member, and said rod having a pair of ends which may be spread apart to permit insertion of said lens member in said grooves.

' CHARLES H. BACHMAN. 

